Unstable High RPM

[helpme]

Hi ya'll. Have a problem with unsteady high RPM about 2500. It oscillates up and down 300 or so about every second. Seems to manifest itself when warmed up. Low idle is pretty smooth. Checked vacuum and no change between warm and cold.
Thought maybe it was the cat clogging up but changed cat and no effect. No CEL on this OBD1 engine.
Is this the fuel pump not keeping up? Fuel filter recently changed.Thanks.

 

[Rearanger]

Have a problem with unsteady high RPM about 2500. It oscillates up and down 300 or so about every second.

2500 under load or just in neutral? Up hill worse?

 

[helpme]

In neutral

Feeling some surging at highway speeds, some loss of power. Cleaned the MAF and IAC. But didn't touch the TPS. I'm thinking the O2 sensors may be bad or need cleaning. Will pull them today. Ran Seafoam thru it and no help. Maybe need to reset the computer.

 

[JP02XLT]

If your CEL light is not on, and no codes set, its not a sensor issue. Have you checked the air filter / intake tube? my neighbors F150 did a similar deal and we found a big nest inside the air box and it was choking it off on air.

You can do a fuel pressure test on the pump to tell its condition

JP02XLT

 

[helpme]

Sometimes you crank it up...

and it'll run real smooth. But I'll check that. Thanks.